The present invention relates in general to active bolsters for occupant crash protection in automotive vehicles, and, more specifically, to preventing an impacting occupant from sliding off of an active bolster instead of being cushioned by it.
An active bolster is a vehicle occupant protection device with a gas-inflatable bladder to absorb impacts and reduce trauma to occupants during a crash. As opposed to deploying air bag cushions through various openings, active bolsters use the interior trim surface itself to expand at the beginning of a crash event for absorbing the impact and dissipating energy through the action of an inflation gas. Co-pending application publication US2011/0316300A1, filed Jun. 26, 2010, entitled “Active Knee Bolster for Automotive Vehicle,” which is incorporated herein by reference in its entirety, discloses an active knee bolster integrated into a glove box door that is light weight and visually attractive.
In a typical structure, an active bolster includes a front wall or panel that faces a vehicle occupant and that attaches to a back wall or panel along a sealed periphery. One or both of the walls is deformable in order to provide an inflatable bladder. The walls are initially spaced apart while in their non-inflated condition. This allows ingress of the inflation gas in a manner that achieves an even inflation across the panel.
The front and back walls of a typical active bolster are comprised of molded thermoplastics such as polyethylene, polyolefin, or PVC. They can be blow molded or injection molded. As a result of having spaced apart walls, an “oil-canning” effect can become a problem. Oil canning is the springing in and out of a flat panel perpendicular to the plane of the panel. In addition to creating a drum-like noise, oil canning is undesirable because it gives a perception of lack of structural quality and integrity. Furthermore, vibrations during operation of a vehicle may become concentrated at the bolster, thereby creating additional noise. As disclosed in co-pending U.S. application publication number US2011/0316300A1, the inner field of the bladder walls may contain a plurality of interconnections to improve rigidity and avoid oil canning. Since the front wall moves away from the back or back wall during inflation, the interconnections between the walls must tear or separate during inflation. As previously disclosed, the interconnection between the walls have been made strong enough to avoid oil canning while being weak enough to avoid interfering with or slowing any part of the inflation.
Since the typical bladder formed by the front and back walls of the bolster is relatively flat and is joined around the periphery by a seal that remains unbroken, a greater amount of expansion (i.e., movement of the cushioning surface toward the occupant) has been produced at the center of the bladder than at the periphery. Thus, the edges of the inflating bladder have been sloped such that the impacting body of an occupant may tend to slide away from the bolster if the main impact occurs at the edges. In order to avoid this problem, the overall area of coverage (e.g., width) of the active bolster has been made large enough to contain all expected impact points to be within the edges of the bolster based on the potential sizes and positions of occupants. However, an extra size of the bolster increases its cost and constrains the styling and appearance that can be designed into the automotive interior.